Keep in mind when planting that Black Prince is thought of as very hardy, so this plant will tend to go dormant over the long winter months. Planting Black Prince in loamy soil with a ph of between 6.0 and 7.0 is ideal for as it does best in weakly acidic soil to neutral soil.
By our calculations, you should look at sowing Black Prince about 56 days before your last frost date.
As Black Prince is very hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.